Jaw crushers for breakage of materials are known in the art. Such apparatus includes two opposing supporting members known as jaw stocks, which are generally angularly disposed relative to each other, and which can be moved relative to one another by the motion of at least one of the jaw stocks. In normal circumstances the jaw stocks are generally plate-like and are arranged so as to define a tapering channel region therebetween. Also, the opposing faces of each jaw stock are generally fitted with a removable wear plate made of a hard, wear resistant material which is clamped thereto, to prevent abrasive damage to the jaw stocks during use of the crusher. These jaw stock faces which are fitted with the wear plates are known as the ‘front inner faces’.
When preparing a jaw crusher for use, in some cases a wear plate is lowered into position on a sloping jaw stock surface and is initially retained in this position (to avoid dislodgement) by various flanges or shoulders that are either formed with, or welded or otherwise fastened to the said opposing front inner faces of the jaw stock pair. In some cases the wear plates have been cast with complementary recesses or slots to enable such retention to occur. At this point bolts or screws can then be inserted via the jaw stocks to clamp the wear plates in position. However, if the clamping fasteners or the supporting flanges or shoulders are damaged or become worn due to exposure from the flow of material across the wear plate, the wear plate can break free and become dislodged.
In use, relatively coarse feed materials such as rock, gravel, mineral ores and the like are passed under the influence of gravity into the channel formed between the wear plate/jaw stock pair and the motion of the or each jaw stock causes the feed materials to become crushed therebetween. The materials are thus comminuted or crushed to the point where they of a particle size small enough to pass through the distance between the wear plate/jaw stock pair, and consequently these materials then fall out of the base of the tapering channel region.
The surface of the wear plates are subjected to significant and uneven wear from the impact and sliding movement of feed material. Such wear plates can be made of an impact and wear resistant material such as manganese steel, whereas the jaw stocks are typically made of a relatively lower impact and wear resistant metal, which can more easily become damaged. It is impractical from both a cost, duty and repair perspective to manufacture the jaw stocks from the same impact and wear resistant material as the wear plates are made from.
After a period of time the wear plates become sufficiently worn due to impact and abrasion to require replacement. Since each wear plate is clamped to a respective jaw stock by various bolts or other types of fasteners located through the jaw stock itself, replacement maintenance requires that the crusher operation be stopped and the respective wear plates unscrewed or unbolted from the jaw stocks. Normally this is done by accessing the back outer face, of each jaw stock, i.e. via those sides of the jaw stocks that do not face toward the tapering channel region. This then allows removal of the worn wear plate from the front inner face of the jaw stock.
In the case of a movable or reciprocating jaw stock, the back outer face access can be obstructed by the crusher drive mechanism (or other mechanism or assembly) which may be required to cause the reciprocation of this jaw. It is also frequently the case that the fixed jaw stock is positioned immediately adjacent to major obstructions in the region of its back outer face, for example other pieces of equipment such as feeders (for introducing feed material into the crusher), walls, and so on. This can mean that the removal of the wear plates necessitates first moving surrounding steelwork and accessory items such as feed or drive mechanisms, chutes etc, or moving the whole jaw crusher from its in use position.
Alternatively, even if access to the fastening means can achieved with difficulty in confined and awkward spaces within which there are moving components etc, then this practice materially increases the hazards associated with such repair work. An example of where restrictions in space can cause such obstruction to the back of the fixed jaw stock include where a jaw crusher is positioned as part of a transportable and mobile crawler crusher unit within which the components of the total crusher assembly are tightly placed to achieve the smallest possible overall dimensions for the machine.
Frequent replacement of these wear components first involves stopping the jaw crusher and manually removing the various parts. This can be a complicated, awkward and difficult procedure especially with regard to the fixed jaw stock for the reasons already mentioned, leading to significant down time of the crusher. A high frequency of maintenance shutdown can be very costly from an operational standpoint.